Cell transplantation is increasingly becoming a therapy of choice for a variety of cell-based disorders ranging from sickle cell anemia and diabetes to Parkinson""s disease. For example, cell lines may be transplanted to deliver a biologically active agent such as insulin, for the treatment of diabetes; parathyroid hormone, for treatment of hypoparathyroidism; erythropoietin, for treatment of anemia; and gamma-amino-butyric acid, for treatment of epilepsy. The cells may naturally secrete the biologically active molecule, or be genetically modified to do so. There are several obstacles that prevent cell transplantation therapy from realizing its full potential. For example, obtaining quantities of cells suitable for transplantation is often a problem. Cell lines transformed with oncogenes can pose a risk of unwanted cell migration, unrestricted proliferation, and possibly tumor formation. Transplant rejection is also a potential problem. These problems have been addressed by encapsulating the transplanted cells in immunoisolatory vehicles which retain the cells at a desired location within the transplant recipient, where the cells secrete the biologically active substances. The immunoisolatory vehicle prevents unwanted cell migration, possible tumor formation, and reduces the possibility of transplant rejection. Methods of transplanting encapsulated cells are disclosed in U.S. Pat. No. 5,550,050.
For some cell-based disorders, it is necessary for the transplanted cells to become integrated with the host tissue being treated. In these cases, encapsulation methods cannot be used. Thus, it is important that the transplanted cells are human leukocyte antigen (HLA) matched to the patient""s tissue to reduce the likelihood of transplant rejection. Hematopoietic stem cell transplantation, is an example of a therapy where donor cells become integrated with the patient""s own tissue. It is an effective therapy for a number of diseases, such as sickle cell anemia, aplastic anemia, and a variety of immunodeficiency disorders, including those which result from treatments for other disorders such as chemo- and radiotherapy treatment for cancer (reviewed in Amos and Gordon, Cell Transplantation 4(6):547-569 (1995)). Hematopoietic stem cells, are present in adult bone marrow and blood (in smaller numbers), and are capable of giving rise to all of the cells of the hematopoietic cell lineage. Fetal sources of hematopoietic stem cells in umbilical cord blood and liver, have also been reported. Lu et al., Critical Rev. in Oncol./Hemataol. 22:61-78 (1996).
Certain neurological disorders treated by cell transplantation, also require that the cells become integrated with the host tissue. For example, in the treatment of myelin deficiencies, it is necessary for the transplanted cells to reform the insulating cellular sheaths around the axons of demyelinated neurons. Animal models of myelin deficiencies have shown promising results from the transplantation of undifferentiated neural stem cell progeny into demyelinated regions of the central nervous system. Hammang et al., Experimental Neurology 147:84-95 (1997).
Several tissues in the body contain stem cells. The primary role of stem cells in adults is to replace cells which have been lost by natural cell death, injury or disease. Stem cells have been defined as xe2x80x9cundifferentiated cells capable of a) proliferation, b) self-maintenance, c) the production of a large number of differentiated, functional progeny, d) regenerating tissue after injury, and e) a flexibility in the use of these optionsxe2x80x9d. Potten and Loeffler, Development, Vol. 110, ¶. 1001-1020 (1990). Stem cells isolated from the early embryonic blastula, i.e. prior to gastrulation, can produce cell types of all different lineages (for review see Keller, G. M. Curr. Opin. Cell Biol. 7:862-869 (1995)). More recently, it has been hypothesized that neural tissue is likely to be the default state for all cells during early embryonic development. Green, Cell 77:317-320 (1994); Hemmati-Brivanlou and Melton, Cell 88:13-17 (1997). However, in the adult, it is generally believed stem cells present in a specific tissue are restricted to produce cell types of that tissue. For example, hematopoietic stem cells derived from adult bone marrow give rise to progeny of the blood, immune system, and myogenic precursors, but have not been reported to give rise to other tissue types. Ferrari et al. Science 279:1528-1530 (1998). Similarly, adult neural stem cells obtained from neural tissue have only been reported to give rise to neural specific cell types.
In addition to the treatment of various cell-based diseases and disorders, cell transplantation could also be potentially useful for treating injuries and/or strengthening, or otherwise, augmenting various tissues such as, skin, heart muscle, and bone. However, lack of availability of sufficient quantities of compatible, healthy cells of the required phenotype, which can become integrated with the desired tissue, prevents cell transplantation therapies from reaching their full potential. For example, in the treatment of bone marrow diseases, it is difficult to find well-matched donors who are willing to be subjected to the painful and time-consuming bone marrow donation process.
A reliable source of cells that can be used for transplantation, with reduced risk of rejection, to replace or augment cells in a variety of tissues is needed.
It is an object of the invention to provide a source of stem cells that can be used to augment any type of mammalian tissue including, but not limited to, bone marrow, liver, thymus, spleen, pancreas, heart muscle, lung, skin, skeletal muscle, smooth muscle, gonadal, intestinal, central nervous system (CNS), and lymph tissue. It is also an object of the invention that the stem cells be obtainable from autologous, allogeneic, or xenogeneic tissue, and readily proliferated ex vivo to generate a sufficient number of cells for tissue augmentation.
These objects are achieved by providing methods for augmenting one or more tissues of a mammal by administering multipotent neural stem cell (MNSC) progeny to the mammal and allowing the MNSC progeny to integrate with the tissue. The MNSC progeny can be administered to the mammal by any suitable method. For example, the cells can be administered systemically, where they migrate to tissues requiring augmentation, they can be applied close to the periphery of the tissue to be augmented, or injected or applied directly to the tissue to be augmented. In the treatment or augmentation of CNS tissue, MNSC progeny can be administered outside the CNS, and migrate to the CNS and differentiate into CNS cells.
Methods for generating differentiated non-neural mammalian cells from MNSC progeny are also provided which comprise placing the multipotent neural stem cell progeny in an environment that induces them to produce the differentiated non-neural cells.